Corrosion inhibitor



Feb. 23, 1943. E. R. DARBY ErAL 2,311,644

CORROSION INHIBITOR Filed Dec. 1'7, 1938 2 Sheets-Sheet l N A@ manor z wmp n 29.2%@ om. mm. oo. n om mm ATTORN EYS Feb. 23, 1943. E. R. DARBY ET AI. 21,311,644

CORROSION INHIBITOR Filed Deo. 1?, 195s 2 Sheets-sheet 2 INHIBITOR 36 SEA SALT WATER MANGANESE BRONZE PROPELLERS MONEL METAL SHAFTS MALLEABLE IRON INHIBITOR IRUI INHIBI'IDR IRON INHIBI'IDR INHIBITOR NI KEI.

fao-2o) DURATION TEST IN CAST IRON INHIBITOR ZINC INHIBITOR MANGANESE BRONZE PROPELLERS coeAcr NICKEL mman-mn (eo-20) COBALT INHIBI'TOR DURATION 0F TEST IN HOURS ATTORNEYS Patented Feb. 23, 1943 COBRO SION IN'HIBITOR Ernest R.. Darby and Philip J. Potter, Detroit, Mich., assignors to Federal-Mogul Corporation, Detroit, Mich., a corporation of Michigan Application December 17, 1938, Serial No. 246,416

(Cl. 204-148) Y Claims.

Our invention relates to corrosion inhibitors. It has to do particularly with the provision of an inhibitor for use in connection with articles of copper or copper alloys which are subject to corrosion as the result of use in salt water, although it is not necessarily limited thereto.

In the prior art, various corrosion inhibitors have been utilized with some degree of success. Among these are inhibitors formed of cadmium, zinc, cadmium-zinc, malleable iron, cast iron, Armco iron, and iron-copper alloys with the copper content ranging up to per cent.

One of the objects of this invention is to provide a corrosion inhibitor which will more effectively inhibit corrosion than those inhibitors previously used in the prior art.

Another object of this invention is to provide a corrosion inhibitor which will be relatively'inexpensive and readily formed and which will have va comparatively long life.

a corrosion inhibitor` particularly suitable for use in connection with propellers and impellers containing copper which are designed for use in salt water.

Uur invention consists primarily in the discov-v.

We have found that cobalt alone may be used.`

However, our tests indicate that cobalt combined with from .5 to 10 per centof nickel is substantially as good as pure cobalt and is cheaper. Likewise, these tests indicate that molybdenum may be substituted for all or part of the niclrel,`

in substantially the same percentages.

Thus, we have found that inhibitors formed of cobalt and cobalt-nickel, cobalt-molybdenum alloys of the type indicated only corrode about onefourth as fast as other known inhibitors such as inhibitors made of cadmium, zinc, cadmium-zinc, malleable iron, cast iron, Armco iro'n, and ironcopper alloys. In inhibiting corrosion of propellers containing copper, such as aluminumbronze propellers or manganese-bronze propel- 1ers, or in inhibiting corrosion on Monel metal shafts, we have found that the inhibitor may be mounted on or form a part of either the propeller or the shaft. However, it is preferably mounted upon the propeller and may, if desired, be shrunk upon a washer which is L-shaped in cross section and which has been previously threaded onto the l nickel alloy or the cobalt-molybdenum alloy, it

, Another object of this invention is to provide' is possible to obtain effective results with larger percentages of either nickel or molybdenum or both. Thus. it is within the scope of our invention to use as much as 20 per cent of nickel or molybdenum or both in combination with the cobalt.

The exposed area of the inhibitor is of importance. Thus, in the application oi' our inhibitorto a shaft and propeller, both containing copper, we have provided the inhibitor with an exposed immersed area 'of the inhibitor approximately I of the area of the propeller. With a Monel metal shaft and an aluminum-bronze propeller rotating for 160 hours in a solution of 8 per cent sea salt in water, there was no loss in weight of the shaft or of the propeller and almost no loss'in weight of the inhibitor. Under the same conditions with an identical propeller and shaft andusing a cadmium-zinc inhibitor embodying i7 per cent zinc there was no loss in the weight of the propeller but there was a loss in weight of the inhibitor of .86 gram. With the same shaft and propeller rotating for thersame period of time in the samesolution and using a cast iron inhibitor there was a. loss in weight of the inhibitor of .82 gram. With a Monel metal shaft and a manganese-bronze propeller, with the same solution and for the same period of time with-other conditions being the same and with using a malleable iron inhibitor there was a corrosion of the inhibitor which resulted in a loss in weight thereof of 1.27 grams.

t In order to illustrate the importance of corrosion inhibitors and, more particularly, the comparative advantages of the cobalt-base inhibitors which form the subject matter of our invention, we have appended hereto drawings constituting reproductions of three charts and respectively designated Figures 1, 2 and 3. The charts f show propeller corrosion with and Without the use of inhibitors, and the rates of corrosion of various inhibitor metals in plain sea salt and in a solution of sea salt with ferrie chloride and Rochelle salt.

In Figure 1 it will be noticed that the weight of the propeller actually increases where the inhibitors are used, less so in plain salt water and more so when ferric chloride is added. This is more or leas the same with all active inhibitors, though the curves were plotted from cobaltnickel data. This gain in weight would probably not take place in actual marine service, as there would not be suiicient concentration of the product of inhibitor corrosion to produce a coating. Nevertheless, the comparative results are pertinent.

In Figures 2 and 3 are shown the loss in Weight, due to selective corrosion, of the various inhibitor metals. Figure 2 gives the results in plain sea water and Figure 3 gives the results when ferrie chloride is added. It is interesting to note that in the ferrie chloride solution the corrosion o1' the cobalt and the cobalt-nickel inhibitors increases, while the others `decrease and reverse their relative positions. This we cannot explain, except that it is not at all unusual to ind reversals with the use of different corrosive solutions. However, even here, the cobalt and cobalt-nickel inhibitors are far superior to the others.

In all of the gures we have plotted the intermediate points as falling on a straight line.

' This is not strictly correct, but We have taken enough intermediate points to know that their relationship should be expressed as a straight line if it were possible to eliminate slight errors caused by removing and cleaning the inhibitors for weighing.

Though we have discussed these inhibitors more particularly in connection with propellers and propeller shafts, it will be understood that they have many other possible applications. 'I'hey are applicable to water softener equipment,

electrolytic corrosion occurs, particularly along the seaboard. They are applicable to swimming pool equipment, particularly those handling chlorinated solutions. They are applicable to refrigerator circulating systems employing brine solutions as transfer media. As a matter oi' fact, they are applicable in innumerable branches of the chemical industry.

Having thus described claim is:

l. In a system for use in contact with a vsalt our invention, what we water solution, said system comprising at least one part made from a metal containing copper as a principal constituent which is subject to electrolytic corrosion during normal use of the system in contact with said solution, a'metallic corrosion inhibitor in direct electrical contact with said copper-containing part and adapted to prevent corrosion thereof, said corrosion lnhibitor comprising at least about 80 per cent cobalt. f

2. The system oi' claim 1 wherein said corrosion inhibitor comprises a total amount of from 0.5 per cent to 20 per cent oi' at least one element from the group consisting of nickel and molybdenum, with the balance substantially cobalt.

3. n propeller assembly adapted for use in contact with sea water, said assembly comprising a copper-containing bronze propeller which is subject to` electrolytic corrosion, a shaft for said propeller, and a metallic corrosion inhibitor in particularly of the zeolite type, the parts oi.n

which are chiefly of bronze and are to some extent exposed to saline solutions whether used in domestic or in the industrial field. 'I'hey are applicable to marine condensers, such as are used in connection with marine boilerswhich are, to a large extent, of copper alloy construction and suier from corrosion from salt water used for cooling. They are applicable to aquaplanes or airplanes whose parts come in contact with salt water, since we understand that it is the practice, because of salt water corrosion,

to grind and polish such propellers, et cetera, to eliminate pits therein every several months. They are applicable to deep well pumps, in which direct electrical contact with said propeller andV adapted to prevent corrosion thereof during use, said corrosion inhibitor comprising at least about per cent cobalt.

4. The propeller assembly oi' claim 3, wherein said corrosion inhibitor contains a total of from 0.5 per cent to 20 per cent of at least one metal selected from the class consisting of nickel and molybdenum, and the balance substantially cobalt.

5. The method o1' protecting a. mechanical ele ment containing copper as a principal constituent from electrolytic corrosion during use in .contact with a salt water solution, which comprises maintaining said element .in direct electrical contact with a metallic corrosion inhibitor during contact with said solution, said corrosion inhibitor comprising at least about 80 per cent cobalt.

ERNEST R. DARBY. PHILIP J. POTTER. 

